1. Please navigate to Shopify Admin Page -> Online Stores -> Themes -> Customize:
2. When you're in Theme Editor, click the "3 dots" besides the Theme File name:
   
   
3. You'll then see the Theme Details and the Theme version you are in.
   
   

Other Useful Information:

How to Update Shoptimized Theme - Update theme to Latest Version.

How to Change Specific Colors - Change Specific Colors in the Theme